[Gate-users] Fwd: hits.dat Gate question

Thu Jul 19 21:57:49 CEST 2018

Dear GATE-Users,

the eMail attached I received from Marcin Balcerzyk,
because he could not send it to the Gate-users List.
Maybe this is caused by the fact that he used a different
eMail address before, that from an earlier affiliation.
Please let me know, if somebody knows how to address this
issue.
Also, if you can help him and give advice, please respond
to his eMail (in Cc:) and also to the gate-users list

Many thanks and kind regards,

Uwe Pietrzyk

/----------------------------------------------------------------------
Prof. Dr. Uwe Pietrzyk
Diplom-Physiker

eMail: U.Pietrzyk at fz-juelich.de<mailto:U.Pietrzyk at fz-juelich.de>
eMail: Uwe.Pietrzyk at web.de<mailto:Uwe.Pietrzyk at web.de>

/----------------------------------------------------------------------

Begin forwarded message:

From: Marcin Balcerzyk <mbalcerzyk at us.es<mailto:mbalcerzyk at us.es>>
Subject: hits.dat Gate question
Date: 18. July 2018 at 15:33:00 GMT+2
To: <u.pietrzyk at fz-juelich.de<mailto:u.pietrzyk at fz-juelich.de>>

Dear Uwe.

I subscribe to Gate mailing list but due to various changes in university emails, somehow I cannot post it to the list using my email of mbalcerz at ucm.es<mailto:mbalcerz at ucm.es> (previously mbalcerz at pluri.ucm.es<mailto:mbalcerz at pluri.ucm.es>). I asked the list administrator to fix it, subscribed from my current University of Seville, but there is no answer and I still cannot post. If you are the list administrator, could you fix it? If not, let me ask you the question anyway.

On http://www.opengatecollaboration.org/UsersGuide you are listed as a person compiling User´s Guide for Gate, so I hope I am asking the right person. In 2009 I did an Albira preclinical PET 3 ring scanner simulation with Gate 3 which was working fine, giving correct results that led to publication. So I have confidence in the way the simulation is built. I transferred it then to vGate 1.0 (Gate 6.0.1) in 2010 and did adaptation. It also worked fine. Now I wanted to do some serious research again and use Gate, now using information which comes out of hits.dat file. I read the description of columns: N+8, N+9, N+10 XYZ position of the hit and some other columns in hits.dat.

All output below comes from Gate 6.0.1 (vGate 1.0). Below is the example photoelectric hit list for the crystal containing lutetium (K line at 63.3 keV). I have a problem interpreting the data (in the image of the table below), namely:

[cid:image002.png at 01D41EAC.9BB9A4B0]

  1.  What does really stepLength correspond to? Here it is the distance between (posX, posY, posZ) between two rows. Such a long one should be the energetic electron emitted in PhotoElectric effect, yet particleType is 22 which is photons. So particleType is the type of particle entering i.e. causing the hit?
  2.  Why the ID of the particle is 5 and there is no 3 nor 4 in the hit history? This event did not generate a coincidence and only a single. Can it be that the other single did not reach the energy threshold?

The next hit list is from a Compton event in the crystal detector from the positron annihilation at point (0.0506, -6.086, -6.136):
[cid:image006.png at 01D41EAC.9BB9A4B0]

Here is a drawing in Origin 2018 with the IDParticle as a label. A distant point before label 2 is annihilation, about 75 mm away, so you look along the 511 keV gamma arriving at crystal:
[cid:image009.jpg at 01D41EAC.9BB9A4B0]

  1.  Here starts my problem connecting hits with length, positions and angles. I understand that here the first row is listing in (posX, posY, posY) the location of Compton scatter (labelled small 2). Then the stepLength of 6.445 mm is the length of scattered photon path to the next hit – PhotoElectric event in row 2 . This hit did not have any Rayleigh nor Compton scatter in the phantom before reaching the detector. Yet when you calculate Compton scattered angle of the photon it is almost zero, not the one expected from Compton scattering. How come? Is GEANT4 not simulating Compton events and scattering angles correctly? The scattered electron is the one with 0.262 MeV energy and step length of 0.11 mm?
  2.  I do not know what the stepLength of 4.953 mm with PhotoElectric hit corresponds to. In the material of my detector, the radiation length for 63.3 keV photon is 0.32 mm. So is 4.953 mm corresponding to the distance of emitted electron? It seems too long a distance for a 0.181 MeV electron, if in previous interaction with 0.262 MeV it was 0.11 mm?
  3.  Maybe you can send me a history of some single hit with a Compton in the detector without a Compton in the phantom and annihilation position to make sure I have no problem with my scanner macro?
  4.  The last question is independent of the previous: is there a way to get a hit data (especially hit position and energy lost) for the gammas in a PET scanner that are scattered in the phantom? Shall I execute attachCrystalSD on the phantom as you seem to suggest on the page http://wiki.opengatecollaboration.org/index.php/Users_Guide:Attaching_the_sensitive_detectors ? If so, where the hit data would be stored – in hit.dat or in a corresponding root file (I have both ascii and root enabled)? My phantom is not a voxelized one.

Thank you for your patience. I would post it to the list, but I have no access.

Kind regards

Marcin Balcerzyk, Ph.D.
Unidad Ciclotrón,
Centro Nacional de Aceleradores,
Universidad de Sevilla-CSIC-Junta de Andalucía,
Parque Tecnológico Cartuja 93,
c/Thomas Alva Edison Nº 7,
Tel.: (+34) 954 460 553 ext. 236,
Fax: (+34) 954 460 145,
mobile:(+34) 697 322 126
Skype: balcerzm

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Eingetragen im Handelsregister des Amtsgerichts Dueren Nr. HR B 3498
Vorsitzender des Aufsichtsrats: MinDir Dr. Karl Eugen Huthmacher
Geschaeftsfuehrung: Prof. Dr.-Ing. Wolfgang Marquardt (Vorsitzender),
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